This invention relates to hybrid integrated circuits, which are comprised of an interconnection substrate and integrated circuit chips which are mounted on that substrate, and more particularly to a new universal substrate which can be used to interconnect any desired set of chips by any possibly desired wiring diagram.
An integrated circuit is manufactured together with many other similar circuits within a thin slice or wafer of silicon. The final process step applied to wafer manufacture is to saw or break the wafer into individual circuits or chips. Each chip carries a set of bonding pads through which the chip must be connected to other chips and to the outside world. This can either be done by placing each chip into an individual package, wherein a connection is made between each bonding pad and a corresponding package lead and where further external connections are made between package leads, or by placing chips on a substrate whereon interconnections are made from each chip bonding pad to a corresponding substrate bonding pad and where further interconnections between substrate bonding pads are provided by the substrate. The type of bond (wire, beam lead, gold bump, solder ball) is immaterial in the context of this invention. Wire bonding will be used in the following description of the invention for the purpose of explanation only. If the chips are bonded directly to an interconnection substrate, the whole assembly is called a hybrid circuit. This invention relates to using a silicon wafer similar to those used to make individual chips as a substrate for a hybrid circuit.
In the prior art, substrates, which are usually manufactured as multi-layered ceramic plates, provided a limited number of routing channels for the required chip interconnections. It took, therefore, a costly and time consuming automated and/or manual process to devise a suitable interconnection pattern. Furthermore, since most substrates in a system differ from each other, a separate set of tools was needed for the manufacture of each substrate type.
Accordingly, the primary object of this invention is to provide a universal substrate which can be programmed to provide any desired interconnection pattern between any set of chips which may be placed on that substrate.
Another object of the invention is to provide routing channels of such numbers and such properties that programming the interconnections can be done effectively and without extensive computer aided or manual layout work.
Still another object of this invention is that programming can be done similar to the known capabilities of ROM and PROM chips either by "mask programming" or by "electrical programming" of a completely finished substrate.
Still another object of this invention is to extend the electrical programming to electrical reprogramming so that logic design errors and/or substrate manufacturing defects can be corrected after the substrate has been finished.